Present day intelligent mobile communication devices have evolved from a first generation of digital mobile telephones that were capable of not much more than conveying voice conversations in real time. Now the devices are capable of communicating in packet switched high speed digital mobile networks and capable of processing and presenting data in much the same manner as a personal computer. The field of use now includes a diverse number of types of applications, among which games and electronic commerce are only two.
Needless to say, in order to provide users of these terminals with suitable software for use in such applications, there is a need for the terminals to be able to download software written by third party software developers as well as the terminal manufacturer. This can be achieved by way of removable memory units on which software modules can be stored. An example of such a removable memory unit is the Multi Media Card (MMC), which has become a standard for many applications in the field of portable intelligent devices.
There is, however, a problem with removable memory units such as a MMC. Because of the fact that the memory unit can be removed from the communication device, it is possible to alter the content, using e.g. a PC, and then re-insert it into the terminal and operate the terminal with modified software. Such alterations may be innocent enough. However, in many situations it is essential that the integrity of the software is maintained from the provider of the software. Needless to say, software relating to, e.g., electronic commerce is of a kind that relies on integrity.
Therefore, there is a need of a system which tests for the integrity of the software before the software is allowed to take control of the communication terminal. In one example of prior art systems, the Symbian system, this is solved by way of storing inside a protected storage area in the terminal, a cryptographic hash of the software that is to be run by processing means in the terminal. Each time the software is to be activated, i.e. run in the terminal, a hash calculation is performed on the software data and if the calculated hash does not match a hash value already stored in the terminal, the software will not be run.
However, this Symbian solution has a drawback in that it is not very flexible when a user of the terminal wishes to download additional software applications that have not been subject to the integrity check involving the storage of a hash value in the terminal. Since the additional software has been stored on the removable memory unit by, e.g., a third party software provider at the time when a user has already obtained the terminal from a terminal provider and the software being intended for use on any terminal, there can be no record of the specific software (i.e. no hash value) in the terminal itself. Therefore, there exists a problem of the software not being allowed to run on the terminal or, as the case may be, can be run only as, e.g., “non-trusted” with less than normal capabilities for operating the terminal.